Anisotropic heat conduction in the metal-organic framework perovskites

We report thermal conductivity (κ) measurements on single crystals of the metal-organic framework perovskite compounds [C(NH₂)₃]X(HCOO)₃ (X=Cu, Zn) in the temperature range 5K ≤ T ≤ 300K. The directionality of N-H---O bonds and their stretching due to the Jahn-Teller distortion in the Cu compound are identified as mechanisms underlying differences in κ(T) behavior for the two compounds and its anisotropy. For heat flow along a direction preferentially transverse to the N-H---O bonds, κ≈ 0.6 W/mK near 300 K, approaching the theoretical minimum value. A possible magnetic contribution to the heat flow in the Cu compound will also be discussed.